This invention concerns a leak resistant watch casing designed to accomodate a thin watch movement and comprises a case-band bezel onto which a watch glass is sealed, a back cover snap mounted onto the case-band, a casing ring supporting the movement, an elastic binding of substantially rectangular cross section with a first large side of the rectangle mounted on the periphery of the casing ring and the two smaller sides pressing respectively against the case-band and the back cover when these elements are secured together.
Present day styling calls for watches having greatly reduced thickness and it is by no means rare to find movements mounted in these watches of which the thickness is on the order of a millimeter. Such a constraint in the miniaturisation requires the designer to turn away from classic solutions by far too cumbersome and find original solutions whether this be at the level of the components which form the movement or, as will be seen from the present, at the level of the casing itself.
A watch casing having a certain resemblance to that which is to be described hereinafter is known from Swiss Pat. No. 619 345 wherein the casing ring 7 is covered on its exterior by a sealing number 9 presenting two edges 9a and 9b which extend radially towards the interior and cover portions of the casing ring. This construction, as may be seen from the drawings relating thereto, has obviously not been intended for a thin watch. There will be noted in particular the substantial volume occupied by the edges 9a and 9b and above all the system by which the projections 7a and 7b of the frame are hooked onto the bulges 3b and 4b as exhibited respectively by the case-band bezel 3 and the bottom cover 4, this system being impracticable on a frame of which the thickness would be on the order of a millimeter.
Swiss Pat. No. 310 877 concerns a leak resistant and shock resistant watch-case characterized in that it comprises a casing ring formed by a metallic ring surrounded by a binding of plastic material which is compressible, this binding presenting an exterior edge which is pressed against the case-band by a closing member for the case. This construction relates to a watch of substantial dimensions wherein the binding is mounted in such a fashion that the movement floats within the casing. Such cannot be suitable for watches of small dimensions as currently used where such a construction would prevent a miniaturisation of the assembly, notably by the edge of the binding which inevitably increases the diameter of the finished product. It will further be noted that the cited construction by definition will not permit a precise centering of the movement in the case, and hence is not suitable for a watch at the top range of quality.
U.S. Pat. No. 2,256,200 likewise concerns a shock resistant watch and where consequently the centering of the movement relative to the casing is totally lacking in precision. Moreover it will be noted that the bottom cover is adjusted onto a one piece casing on the interior of which may be supported the elastic binding. This construction in no manner permits the provision of an exterior cut-away on the periphery of the back cover in order to give the assembled timepiece an even thinner aspect as will appear from the present invention. In order that this be possible, it would be necessary that the separation between the back cover and the case be realized at a place where the exterior perpiphery of the binding would cover said separation.
In order to overcome the preceding difficulties there has been proposed in Swiss application No. 631 045 G a watch casing design which may be applied to an extra thin watch. To this end the application discloses a casing ring formed by a metal plate 1 overmoulded by an elastic material 10 while the back cover 5 and the case-band 6 are snapped together. Thus, in this design, the thickness of the overmoulded plate 12 is small and less than two mm. Such a solution however necessitates an overmoulding which, on the one hand, can only be obtained onto a metal plate and, on the other hand, requires that there be provided as many overmoulded components as there are varieties of casing.
Thus, the present invention proposes to overcome the difficulties as cited above by providing a new design provided with means which will appear from the claims.